(1) Field of the Invention
The present invention relates to a display device and a manufacturing method for the same, and in particular, to a display device where an oxide semiconductor is used in the TFT circuit and a manufacturing method for the same.
(2) Description of the Related Art
Various types of display devices, such as a liquid crystal module (liquid crystal display device) and an organic electroluminescent display device, are used as the display device for many portable type information apparatuses, such as a cellular phone, a portable information terminal (PDA), a digital camera and a multimedia player.
An insulating substrate made of glass or a resin is used as a part of the display panel of these display devices, and thin film transistors (TFTs) are formed on the surface of this insulating substrate so as to be used as switching elements for driving the respective pixel electrodes.
The TFTs on the insulating substrate, for example, a glass substrate, data lines for transmitting signals for driving the TFTs, and gate lines for transmitting signals to pixel electrodes through the TFTs are formed on the insulating substrate in a predetermined microscopic pattern through selective etching in accordance with a photolithographic technology using a resist film, such as of a photoresist.
It has been desired to reduce the number of multilayer films and to reduce the number of steps in the selective etching in accordance with the photolithographic technology in order to make the display devices having the above-described structure flexible in order to reduce the cost. Furthermore, it is simultaneously required to increase the aperture ratio of the pixels, which is one important displaying function of the display device.
In recent years, a technology for using an oxide semiconductor layer as the semiconductor layer for forming the channel portion of the TFTs so that the data lines and the pixel electrodes made of a conductive film are directly connected to the oxide semiconductor layer has been used in order to address the above-described desire and request.
Concerning the above-described technology, in JP 2009-99887A, gate lines and a gate insulating film are formed on a substrate, and on top of this, data lines, pixel electrodes and an oxide semiconductor layer are formed so that the oxide semiconductor layer is directly connected to the pixel electrodes and the data lines, which are formed of different conductive films.
In the structure in JP 2009-99887A, however, an oxide semiconductor layer is formed so as to cover the data lines, and therefore, the oxide semiconductor layer can be easily disconnected in the portions where the steps of the data lines make contact with the oxide semiconductor layer. In addition, the pixel electrodes and the oxide semiconductor layer are structurally processed after the formation of the data lines, and therefore, the data lines may be dissolved or corroded by the etchant when the pixel electrodes and the oxide semiconductor layer are formed through etching, and as a result, the possibility of a data line being disconnected and the display performance of the display device significantly lowering increases.